Polyphase x-ray system.



H. C. SNOOK.

POLYPHASE X-RAY SYSTEM.

APPLICATION FILED 1120.26, 1901;

1,131,870. Patented Mar. 16, 1915 2 SHBETS-SHEET 1.

%M% iii? Mi? (574/;

2!: ATTORNEY UNITED STATES OFFICE.

HOMER CLYDE SHOCK, OF PHILADELPHIA. PENNSYLVANIA.

POLYPHASE X-BAY SYSTEM.

Specification o! Letters Patent.

Patehued Mar. 16, 1915 Applicatl'on are. mm zit-190s. Serial 1n. 468,355.

high density and with a substantinlly c011 stunt stream of energypas'sing through the X-re'ytube to maintain u practically continuous excitation at intensity. f I

My invention 'resides also in other features hereinafter describedand claimed.

As stated above, by my'inrention having recourse to apoly-phasejcurrent' supply, an

X-my 'tube'may be excitednt very high intensity with non-intermittent or substantially constant 'streamof energy "passing. throughthe X-miy tubeto maintain a P2116- tically continuous excitation at hi h in tensity. An important technical remltflowing from such a 'system' is at least two fold,

first, notwithstanding the high intensity excitaticnoi the X-ray tube. destruction of theterget in the vicinity of the focus spot by bombardment by cathode particles is prevented or is a considering the great amount of energy liberated; secondly, nctwithstanding the high excitation of the X-ray tube, the vacuum of the tubeis preented froin becoming erratic, that is, either rising or falling suddenly and irregularly, with consequent undesired fluctuations in the quantities and'penetrating powers of the resulting X-rays. Asto the first eflect above referred to, by employing a. polyphase current supply, a given and var large amount of energy is converted into X-rays within the tube withouthowever the occurrence of extreme maximum currents and po tentials which, if occurring, would mechani cally deteriorate the target by pitting ordigging the same by mechanical action. By use of a polyphase system however the relatire fluctuations in the pot'ehtl'al and ouruponthe X-ray tube are low,

tliut is, the maximum current or potential is relatively smaller, for a: given area of energy diagrampr is smaller for a given root-mean square eiiergy'or current value. s me tential; which determines the mechanical force of-impact of-the cathode purtides, and therefore the matter of target destruction, are relatively. low considering the energy delivered through; the tube. And from this reduction in maximum of potential and current, considoring'the energy passed through the tube, the penetration and quantitv ofthe X-rays resulting are far more uniform than in the casemhe r'e the potential andcurrent fluctuatewidely, As-to the second efiect, when there is greet fluctuation in the potential andcurrent, 'in'creased mechanical action upom'thutarget due to the impact of the; cathode particles causes lib- 15 eration into the giissous spice of the X-ray tubiebf a-lergendmber' of finely divi'ded metellic ipurtioles t rom the material of the target at ot' ueun then focus spot.

The result of the' liberation ofnthfese metalso --lic particles is vacuum from moment jbmomenfl duegto} the fiuctuation in the rate absorption oi gasby thiscl'oud of'metullic. nsrticles', withthe result that thcvacuumin thcix ray tub'e hecomes irregulurly higherycausixfg the tube to emit X'-rcy's of irregular-quantity and penetration; Irregularity ef vacuum re- 'sults'alsojbecause of liberation. of gas, either occluded or confined in small spaces or'sacks so within the metal of the target, unto the free gesof the tube, snd'particularly that portion of the volume of the target which has been excavated by the impact ofthe mthode particles.

Further variation in vacuum results from gas liberated from the target from that portion of the volume which is immediately adjacent to the crater excavated at the focus spot of the target.

By recourse to my improved excitation of an X-ray tube, where the differences between maxima and minima of potential and current a're small. the liberation of the cm the undesired efiects above mentioned 15 would be the case where the expenditure of the-same amount of energy in the.X-rayuen'ce the maximum current or po- 60 crgy within'th'e X-ray tube will not clause which:

tube differences between maxima and minima of potential and current are 't. In a practical sense, the result is, briefly, that with a given or ordinary X-ray tube, I can, by my system, without destruction of or injury to the X-ray tube, or without impairing its efiiciency or life passthrough it, in a. given time, greater amounts of energy than has heretofore been possible or the practice, with resultant production of. X-

ravs at greater rate or activity.

For an illustration of one of the forms 11:51 invention may take, reference is to be Figure 1 is a diagrammatic view illustrating the apparatus and circuit arrangements of my system. Fig; 2 is a vertical sectional view, partly in elevation, of a high poten' tial three phase rectifying switch mounted in operative relation with a motor, inverted rotary or other suitable device, and a high potential three phase transformer. Fig. 3 is an end elevational view, partly in section, of the high potential three ham rectifying switch shown in- Fig. 2. ig. 4 is a view graphically repraenting the rectified current waves and their effect in the X-ray tube.

Referring to Fig. 1, L and L are the condoctors of an electric sufpply circuit leading to the motor side M o a motor generator or inverted rotary R, whose generator side G delivers three phase alternating current to the three conductors 1, 2 and 3, a. revers ing or pole changing switch A bem connected n the conductors 2 and 3 or reversing the direction of energy flow 1n the X-ray tube X if for any reason it be in the wrong direction.

In each of the conductors 1, 2 and 3 is inserted an adjustable non-inductive resistance 4 for maintaining the resistances of the three transformer primary circuits 1. And thethree movable contacts for ad usting the resistanca 4 are preferably mechanically connected together, so as to insert or remove equal amounts of resistance in each primary. The conductors I, 2 and 3 lead to the primaries p ,.p and p, of the high potential step up transformer T, each being adjustable as to its number of turns, the three movable contacts for this purpose being preferably mechanically connected together so that the number of turns in the primaries is varied equally. These primaries are here shown connected in Y arrangement, though it is to be understood that the delta connection may be employed.

The high potential secondaries s, s and s are here shown as Y connected, as the preferred connectionthough the delta connection is within my invention. The three phase transformer T having these three primary and secondary windings is of the vthe purpose pf the accompanying drawings, in"

to support the hi closed magnetic circuit type and has a minimum or practically purposes hereinafter referred to. The neutral or common point of the three secondary windings, when Y connected, is connected by conductor 5 to earth or ground at 6. And for this reason the Y connection-is preferred. V From each secondary winding 2', s" and s" a. connection is made through conductors It, h and It to'pairs of conducting arcs of the rectifying switch E, a choke coil D intervemng m such connection if desired, for

preventing any high freency osclllagons (the coils D being high frequency cho ecoils) from running back to the transformer windings where they might cause insul tion punctures or breakdowns.

From the opposed arcs of the rectifying switch extend conductors 2 and 2" leading respectively to the cathode is and anode j of the X-ray tube X.

An ammeter F is connected in series with the tube X to measure the current consumed therein, such amm eter being, for example, of the type described in Letters Patent of the United States No. 768,957, heretofore granted to me.

Referring to-Fig. 2, a bench or base H, of wood or other suitable material, serves 11 potential rectifying switch E, the trans ormer T (contained in the metal transformer case I, containing oil) and the motor generator or inverted rotary R. As here represented, R is an inverted rotary receiving direct current and delivering three phase alternating current. A wooden spindle or shaft J has'metal shaft terminals m, m havin bearings 11, 'n. supported by the end wali o, o of the wooden covering or casingwhich incloses the hi h potential polyphase rectifying switch ()ne of the terminal shafts m is connected by an insulating coupling p with the shaft 9 of the inverted rotary R. Extcnding through and carried by the spindle J are six metallic rods or wires r, s, t, u, o, and 20, each incascd in rubber or other insulating covering and support 2:. The wooden spindle J insulates each of these six rotating cross connectors or other, and the insulating covering 2:, preferably of hard rubber, insulates each of the cross connectors to prevent premature or undesired sparking during operation. These six cross connectors or metallic rods are divided into three pairs, the cross connectors of each pair being disposed at right angles with each other, but the'cross connectors of the second pair progress at an angle of mechanical degrees with respect to the cross connectors of the first pair, and the cross connectors of the third pair progress at an angle of 60 mechanical degrees with the cross connectors of the second pair or at an no magnetic leakage for rods from every le of mechanical degrees with the i d ss connectors of the first pair.

CoBperating with the cross connectors r,

the terminal of another high potential secondary which connects to the neighboring conducting arcs 11 and 13 opposed to the conducting arcs 12 and 14, the cross connectors z and u cooperating with these opposed airs of arcs. Similarly, through the msu lilting tube 21 extends a conductor it com municating with the terminal of the third high potential secondary winding ofthe transformer T, the conductor 1& being con nected to the arcs 15 and 17 which are opto the conducting arcs 16 and 18 respectively, the cross connectors 'v and w cooperating with these opposed pairs of arcs. The cram connectors 0 not touch the arcs in passing them, short air gaps intervening over which the current sparks The conducting arcs 8, 14, and 16 are electricall connected to ether and to the conductor 1. and, as seen in Fig. 1, to the anode of the X-ray tube X. And the arcs'IO, 12, and 18 are connected together and to the conductor i which connects with the cathode is of the l e h hbo f th tween t e neig pairs 0 e lower conducting ans, as ii ewed in 2, which may be styled the supply arcs, since they are connected to the supply side of the switch E, are di the insulating bar'- riers 22 and 23, o mica, micanite, glass, or any suitable highly insulating material. And between the upper conducting arcs 8 and 10, which are on the distributing side of the switch E and may, therefore, be styled distributing arcs, is a g barrier 24; and between the distributing arcs 12 and 14 is a similar in; sulating barrier 25; and betwaen the distribut' arcs 16 and 18 is a similar insulating barrier 26. These insulating barriers are supported, spaced and held in lace by suitable means comprising vertica y extending rail $12.7 and 28, preferably of insulating ma- The conducting arcs 7 and 18 inclusive, are supported upon the tubes 29, 30, 31, 32, 33, and 34, of porcelain, or'other insulating material, disposed upon the parallel rods And these cross connectors and their coverings and the wooden spindle J are all mechanically balanced so that the center of gravity of themoving system is in the axis of the rotating spindle J. The spindle J being preferably mechanically connected to the rotating member which generates the three phase alternating current, insures that the rotating cross connectors are in exact synchronismwith the alternating current delivered from the alternating current side of the inverted rotary R. Or, if the alternating current generator be driven by other means, the spindle J is nevertheless preferably mechamcally connected to the rotating element of the alternating current generator.

The conducting arcs, as here shown, for a three phase system, have an angular extent of something preferably slightly less than 60 mechanical degrees, 60 mechanical degrees in the switch E corresponding with 120 electrical degrees. It follows, therefore, that'since the cros connectors of the difierent pairs are 60 degrees in advance or in arrears of each other, it means that these cross connectors are disposed at an angle of 120 electrical degrees with respect to each other, the same being the interval in electrical degrees between the difierent phases of a symmetrical three phase current.

The operation is as follows: The operator brings the motor M of theinverted rotary into communication with a source of current and brings the inverted rotary or p223 alllzfn nating current erator u to s t us nerating thre phase cui'i'ent of desired equency and rotating the cros connectors of the rectifying switch E in synchronism with that current. The transformer T then delivers hightential three base current which is rec ed by the switc E and sup plied to the tube X. Thus, assuming the cross connectors 1-, s, t, u, c and w to be totating in a clockwise direction, as viewed in Figs. 1 and 3, the cross connector w is just be to admit current from secondary a throng arcs 17 and 18 to the one terminal k of the X-ray tube X. Its companion cross connector '0 is out of circuit as is also the cross connector u associated with the secondcry a. Cross connector t is just leaving arcs 11 and 12, having heretofore admitted current from the secondary s to the terminal ll: of the tube. Cross connector 8 is out of circuit but its associate r is admitting current from secondary 8" through arcs 7 and 8 to the other terminal j of the X-ray tube. As these cross connectors continue to rotate they keep passing both the positive and negative current waves of each phase through the tube X all in the same direction; and more than this, they correlate and superimpose the different h'ulf waves of the phases so that for certain periods of time a plurality of phases coiiperates withpeach other in impressing energy upon the tuhe X all in the same direction, whereby the tube is always traversed by energy, and the minimum potential to which the tube is subjected is greater than the maximum potential delivered by any one of the secondaries alone. The energy is all passed through the tube X in the same direction, the energy of each half wave of each phaseheing thro the tube all: all in the sametyrectliollxieeexcitin thetu to mtens1 an p ng th excitation fifirys-at'a high there being no time when there is no energy passing through the tube. And the mimm'um en at any is suflicient to fullyexcitethetube Asseenfi'omFi, cus c ew: the over p 'walvesa, c, an 02,1 0, b an; a representing the three difierent p aflb andc indicatetlierehtifiedor turned over' n five (for .exam is halfwaves.- And the ength of the con arcs of the switch E being'y electncal degrees, and the angnlarrelation of the cross connectors with to the on the rotatingmember of the alterna current generator is so chosen and fix that each crow connector is active or n circuit for a time corresponding with the distance d. There 'rsults' then inthe circuit of the tube X a fluctuating current'of frequency triple the ency of a half cycle-of one'phase suppli by the transformer T, this triple ueney current being rep ism e 1131 the upper 't of Fig.4. This curve is obtained by a ding the ordinates of the curves below. during such periods as the diferent phases are actively in circuit as controlled by the switch E. It will be noted, therefore, that the potential upon the terminals of the tube X, represented by the distance f, is greater thanthe V tential of anyone of the secondaries of e transformer T. potential" f is dependent upon the maximum of a phase mul' tlal tiplied by twice the'sine of half the angle between the phases. This curve shows that the tube X is constantly subjectedto a potential whose minimum is f and which is always terthan the potential delivered by one 3% of the transformer T, and this minimum potential V thetube X to very high intensity. This potential varies as shown by 'the upper curve e so that the energy through the tube X fluctuates', but at no time has it a potential less than the potential f.

By having practically no inductance in the circuits of the primaries of the transformer '1, other than their own-inductanccs, and by making the transformer T of a minimum or practically no magnetic leakage, and by mechanically connectin the shaft J to the rotating element of the evice generating the alternating current, I secure a maximum elliciency of conversion, along with an excitation of the tube X to'an intensity which has never heretofore been atintensity,

'ment' and f is suflicient to excite I tained, the features enumeratedcontributin to this result, and especially to the resui of preventing inverse discharge in the tube X, inverse discharge being'energy flowinge in the wrong direction through the tu X.

low

The transformer may have ve at'in magnetic leakage, as above stated, so

operationv the spark drawn between a cross connector and its arcs be lon drawn out after thecrom" connector" has eft the trailing tips of the arcs. "However, where this drawing-outset the'sparksis'to be al tween eachother, and to take care "of any' other departures from the ideal conditions.

While I have here illustrated my invention as involv a three phase current, itis. to be und that my invention reters to pol hase currents in general, such as quar ter-p use or two phase currents or currents of other phase relations and numbers.- And while I have shown .theconducting arcs of the switch E in alinement, it is to be understood that they may be disposedlout of alinethe crux connectors suitabl changed intheir relations to the'arc's It is to beunderstood also that the arcs-may be otherwise disposed, in which case a greater number of in'sulating barriers may be re qnired. In the arrangement a of five insulating barriers is required, and this with the alinement of the conducting arc makes the size of the rectifying switch a minimum for any given potenwhat I claim 1. In an X-ray system, the combination, with a source of polyphase alternating current, of a step-up transformer supplied. by said source, a high potential polyphase rec tifying switch driven in synchronism with said current deriving energ from said transformer, and an X-ray tube continuously traversed bythe uninterrupted imidirectional current derived from said switch. 2. In an X-ray system, the combination with a source of polyphase current, of aste up transformer, an X-ray tube, and a hili potential polyphase rectifying switch intervening between said transformer and said tube, said switch causing overlapping uni-' directional current waves to beimpre$ed upon said tube, whereby said tube is coii-' tinuously subjected to a potential higher than the potential of any phase supplied to said rectifying switch.

A system for producing X-rays of high intensity and greater uniformity in characan arc bein substantially equal to the time' of non-over apping of a wave of one phase with respect to a wave derived from another phase.

5. In an X-ray system, the combination with a generator of polyphase'current, of a a polyphase transformer, an X-ray tube, and a high potential polyphase rectifying switch zintervening between said transformer and said tube, said. switch comprising relatively rotatable arcs and cross connectors, the movable element of said switch being mechanically connected to the movable element of said generator.

6. In an X-ray system, the combination with a source of polyphase current, of a 80 polyphase transformer, an X-ray tube, and

a polyphase switch interveni'nr between said transformer and said tube, saYd' switch being driven in synchronism with the polyphase current, and said transformer having practically no magnetic leakage whereby short circuiting between difierent phases is prevented. I

7. In an X-ray system, the, combination with a source of polyphase current, of a 9 polyphase transformer, an X-ray tube, and a r-polyphase switch intervening between said transformer and said tube. said switch comprising conducting arm and cooperating cross connectors so disposed that 43:15:83 is continuously posed thro h id 8. The combinatibn with a source of polyphase current, of a polyphase transformer,

an X-ray tube, and a polyphase rectifying .swjtch intervening between said transformer and said tube, mid switch comprisingconducting arcs and cooperating cross connectors so disposed that energy is continuously passed through said tube, the minimum potential to which said tube is subjected being greater than the potential of any phase.

9. In an X-ray system, the combination with a source of polyphase current, of n polyphase transformer, an X-ray tube, and a polyphase rectifyingswitch intervening betwe'en said transformer and said tube, said tube being continuously subjected to a. poirntial whose minimum is dependent upon a potential which is twice the sine of half the angle of phase difierence between the respective phases multiplied by the maximum otential of a phase.

i 10. an X-ray system, the combination with a source of polyphase alternating current, of a polyphase step-up transformer having low magnetic leakage, an X-ray tube, and a high potential polypbase rectifying switch intervening between said trans former and said X-ray tube.

11. In anX-ra system, the combination with a machine elivering polyphase alternatin current, of a step-up polyphase t ormer, an X-ray tube, a high potentialpolyphase rectifying switch intervening between said transformer and'said X-ray tube, and a mechanical connection between the rotating elements of said machine and said polyphase rectifying switch.

12. In an X-ra system, the combination with a machine elivering polyphase alterail 11151? curren t, of a step-up polyphase ormer having low magnetic leakage, an X-ray tube, a high potential polyphase rectifying switch intervening between said transformer and said X-ray tube, and a mechanical connection between the rotating elements of said machine and said polyphase rectifying switch.

13. In an X-ray system, the combination with a source of polyphase alternating current, of a step-up, polyphase transformer, a high potential polyphase rectifying switch comprising pairs of opposing supply and conducting arcs, a crossconnector associated with each pair, a (pair of supply arcs connected together an to each transformer secondary, an X-ray tube, one terminal of said X-ray tube connected to half of the distributing arcs, and the other terminal of said X-ray tube connected to the remainder of said distributing arcs.

14. In an X-ray system, the combination with a source of polyphase alternating current, of'a constant potential step-up transformer, a high potential polyphase rectifying switch comprisin a plurality of pairs of supply and distn uting arcs, a crossconnector for each pair of arcs, the supply arcs associated with the transformer secondcries, an Xray tube, half of the distribut- I15 ing arcs connected with each other and with one terminal of said X-ray tube, and the remainder of said distributing arcs connected with each other and to the other terminal of said X-ray tube.

15. In an -ray system, the combination with a source of polyphase alternating current, of a high tension step-up transformer, an X-ray tube, and a synchronously driven high potential lyphase rectifying switch 125 comprising con ucting arcs and associated cross connectors, a pan of supply arcs for each phase, a pair of distributing arcs for each phase, the arcs and their cross con-.

ncctors being so disposed that energy from high potential l both the positive angssngative half waves of all the phases is p through said tube all in the same direction.

16. In an X-ray system, the combination with a source, of polyphase alternating current, of a high tension step-up transformr, an X-ray tube, and a 359 a 7 comprising con uctmg arcs and emaciated cross connectors, a pan of supply arcs for each phase, a. pair of distributing arcs for each phase, the arcs and their cross connectors so disposed that energy from both the positive and negative half waves of all the phases is passed through said tube all in the same direction, a of wand its 612s connectors bei a corresponding wi erri e between the phasesof $8.1 d source of alternating current, l

17. In an X-ray system, the combination with a source of polyphase alternating cur rent, of a tension step-up transformer, an X-ray tu and a synchronously driven high potential comprising con uc t mg arcs and associated crcss connectors, a pair of supply arcs for each phase, a pair ofdistributlng arcsior each phase, the arcs and their cross cons nectors being so disposed that energy fr'oni bcth the positive and negative half waves of all the phases is pamed b said tube all in the some direction, and sad tube continuously subjected to a potential at-least as great as the maximum potential of one of the phases.

18. In an X-ray system, the combination with a source of polyphase alternating current, of a h h tension step-up transformer,

an K-ray tu and a synchronously dnven' high potential lyphase rectifying switch comprising con ucting arcs an asociated cross connectors, a pair of supply arcs for each phase, a pair of distributing arcs for each phase, the arcs and their cross connectors being so sad that energy from both the positive an negative half waves of all the phases is passed through said tube all in the same direction, and said tube continuonsly subjected to a tial whose miniimnn exceeds the maximum potential of any phase.

19. In an X-ray system, the combination with a source of polyphase alternating current, of a step-up polyphase transformer, an X-ra tube, and a polyphase rectifying switc intervening between said transformer and said X-ra tube and comprising a pair of supply an dinrihuting arcs and cross connectors for each phase, the supply arcs for each pbam being connected together, and the distributing arcs for each phase being connected respectively to difl'erent terminals of said X-ray tube- 20. In an X-ray' system, a source of threechrono' drivszr hase rectifying switch K former and said phase alternating current, a threehase step-up transformer having its secon aries connected in Y relation, an X-ray tube, and a three-phase recti ing switch mtervenin between said trans ormer secondaries an said X-ray tube comprising a pair of supply and distributing arcs and cros connectors for each transformer secondary, the suppl arcs for each secondary being connec togethcr'and to thatsecondary, and the distributing arcs of each pair being connected respectively to the difl'erent terminals of said X-ray tube.

21. In an X-ray svstem, the combination with a three-phase alternating current genorator, of a threehase step-up transformer, an X-ray tn and a three-phase rectifying switch intervening between said transformer and said X-ray tube and comrising a pair of supply arts and a pair of 51% 'buting arcs an cross connectors for each phase, the supply arcs for each phase being connected together, the distributing arcs for each phase being connected resxpectively to the different terminals of said 1 -ra y tube, and said cross connectors me chamcally connected to the rotating element of said generator.

22; In an X-ray system, the combination with a three-phase alternating current generator, of a three-phase step-up transformer, an X-ray tube, and a three-phase rectifying switch intervenin between said trans -ray tube and comprismg a parr of supply arcs and a pair of distrlbutln arcs and cross connectors for each phase,- 'e supply arcs for each phase being connected together, the distributing arcs for each phase being connected respectively to the difl'erent terminals of said X-ray tube. and said cross connectors mechanicall connected to the element of sai generator, all of said supply arcs being disposed m al1n ement with each other and all the distributing arcs disposed in alinement wig: ealzlch .oger, said cross connelftors for ea-pase inglsposed' atri tanles to each other, and the cross con ectors for the several phases progressing with to each other by an angle correspon ing with the angle between the current phases. A; system of X-ray tube excitation comprising the combination with an X-ray tube, of means delivering high potential polyphase current, and means delivering to 531d tube uni-directional energy of said polyphase current.

24. system of X-ray tube excitation OOmPl'lSlllg the combination with an X-ray tube, of a source of polyphase current, a step-up polyphase transformer deriving energy from said source, a. synchronous high pc-tent1al 'rect1fying switch intervening between sald transformer andseid X-ray tube,

whereby uninterrupted uni-directional en- 130 ergy is passed through said tube and fluctuations in vacuum and deterioration of the anti-cathode of said X-ray tube are lessened.

25. A system of X-ray tube excitation comprising the combination with an X-ray tube, of a source of polyphase current, a step-up polyphase transformer deriving energy from said source, a synchronous high potential rectifying switch intervening between said transformer and said X-ray tube, whereby uninterrupted uni-directional energy is passed through said tube and fluctuation in vacuum and deterioration of the anti-cathode of said X-ray tube are lessened, said transformer having low magnetic leakage whereby short circuiting between different phases is prevented.

26. In a system of X-ray tube excitation, the combination with an X-ray tube, of a source of polyphase current, a step-up polyphase transformer, a high potential polyphase rectifying switch intervening between said transformer and said X-ray tube and comprising pairs of opposed conducting arcs and cooperating cross connectors, a pair of supply arcs for each phase, a. pair of distributing arcs for each phase, the length of each arc in electrical degrees corresponding substantially with the interval between the phases of said source of current, means for driving the rotary element of said rectifying switch in synchronism with the current, said transformer having low magnetic leakage, whereby short circuiting in said rectifying switch is prevented.

27. A system of X-ray tube excitation former comprising the combination with an X-ray tube, of a source of high potential polyphase alternating current, and means for directing through said tube uni-directional uninterrupted energy from both the positive and negative waves of said polyphase current.

28. A system of X-ray tube excitation comprising the combination with an X-ray tubeyof a source. of high potential polyphase alternating current, and synchronous switching means for directing through said tube uni-directional uninterrupted energy from both the positive and negative waves of said polyph se current.

29. A system of' X-ray tube excitation comprising the combination with. an X-ray tube, of means delivering high potential polyphase current. and synchronous switching means delivering to said tube unidirectional energy of said nolvphase current.

30. A system of X-ray tube excitation comprising the combination with an X-ray tube, of a plurality of high potential transsecondaries having a common grounded terminal, and synchronous switching means interposed between the remaining terminals of said secondaries and said X- ray tube .for delivering to said tube unidirectional energy.

In testimony whereof I have hereunto affixed my signature in the presence of the two subscribing witnesses.

HOMER CLYDE SNOOK.

WVitnesses A. E. S'rnnvnocn, DANIEL \VEus'rEn, Jr.

It is hereby certified that in Letters Patent No. 1,131,870, granted March 16, 1915, upon the application of Homer Clyde Snook, of Philadelphia, Pennsylvania, for an improvement in Polyphase X-Ray Systems, errors appear in' the printed specification requiring correction as follows: Page 4 line 105, for the word "arc reed arcs; page 5, line 109, claim 14, strike out the words constant potential;" and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 21st day of September, A. D., 1915.

J. T. NEWTON,

Acting Commissioner of Patents.

[SEAL] 

